How Differential Pressure Affects Blast Equipment

Differential pressure causes 90% of problems with abrasive blasting equipment

Differential pressure is all around us every day. It's what causes the weather to change, it's what makes our ears pop when we drive up hill, and it is also what causes 90% of the problems with abrasive blasting equipment.

A common cause of differential pressure is because the pot is choked. This means that the ball valve on the pusher line is partly closed to assist the abrasive flow. This has been done by the blaster or the pot tender to overcome a negative pressure issue, a leak in the pot seals, or a moisture issue, causing the abrasive to stop flowing out of the blast pot. It is a quick fix which many blasters do every day. Abrasive not flowing by choking the pot for a minute, forces more air into the pot and allows the blockage to be cleared from the system.

If you have a moisture problem, you will find that the blaster operator will:

  • Leave the pot partially choked while blasting.
  • Open the abrasive metering valve more than needed.

Why is differential pressure an issue when blasting?

  • Wasting expensive abrasive media.
    The pot is forcing more abrasive into the air stream than needed. Resulting in the need to purchase more abrasive to complete the project. Also producing more waste that will require larger clean-up and disposal time.
  • Flooding the blasting stream.
    The abrasive is creating higher wear to blasting equipment and lowering its own recyclability.
  • Greater wear on metering valves.
    Forcing larger amounts of abrasive through the metering valve wearing them out more quickly than if you can lower the abrasive flow and still achieve productivity.
  • Lost pound per square inch (PSI) lowers productivity rates.
    The PSI lost because of differential pressure, lowers productivity by 1.5%. This means that a 10 PSI pressure loss will make the job last 15% longer than what is strictly necessary.

Solutions to differential pressure problems.

  • Use a correctly sized and constructed air dryer to rid yourself of moisture problems.
  • Conduct a pressure loss audit all the way from your compressor to your nozzle. Find out where the pressure is being lost so that you can implement a solution.
  • Follow a strict maintenance schedule to ensure that all your valves, pop up seals and gaskets are sealing correctly.
  • Check the ball valve on your blast pot every day before blasting. Look for signs of chocking even to the smallest amount. If it is then you have an indication of something not functioning and may require immediate correction.
Dofferential Pressure choke valve
Blast Pot choke valve